Metal deposition process



Jan. 4, 1955 H. SCHLADITZ METAL DEPOSITION PROCESS 2 Shee'ts-Sheet 1Filed Oct. 16 1950 Jig,- Z

INVENTOR. fi e/"Mann Jc/Mad/fz 1955 H. SCHLADITZ 2,698,812

METAL DEPOSITION PROCESS Filed Oct. 16, 1950 2 Sheets-Sheet 2 1 1 .9.Try I0.

AN xxxyywm IN V EN TOR. Jz'ermann ,Sch lad/f2 United States Patent"Office 2,698,812 Patented Jan. 4, 1955 METAL DEPOSITION PROCESS HermannSchladitz, Munich, Germany Application October 16, 1950, Serial No.190,306 Claims priority, application Germany October 21, 1949 22 Claims.(Cl. 117-47) The invention relates to a process for the production ofmetal deposits, and has for its object to produce by thermaldecomposition of metal compounds completely uniform fine-grained metaldeposits of great adhering strength on substances of all kinds, that isto say, both on inorganic and on organic substances, regardless of theconfiguration of the surface of these substances. In contrast to knownprocesses, this metal deposition is effected with great economy. Aparticular object is to produce metal deposits on heat-sensitive organicsubstances of very fine structure (for example textile fibres orfabrics).

In the process according to the invention, such metal deposition iselfected by separating the metal from the metal compound at such a shortdistance from the surface of the material to be metallized that theagglomeration (coarsening of the grain) of the metal particles beforethey are deposited is prevented, by maintaining the temperature of thesurface to be metallized at an equal level during the separationprocess, and by limiting the maximum heating of the material to bemetallized preferably to the surface layer.

In order that this process may achieve the desired result,

the conditions of dissociation of the metal compound must be maintainedas uniform as possible on or above the deposition surface during theseparation of the metal. The maintenance of constant dissociationconditions in the thermal decomposition of metal compounds is anecessary pre-condition for ensuring a uniform, fine-grained and firmlyadhering deposit.

If it is desired to obtain a fine-grained deposit having excellentadhering strength on any desired materials, including more sensitiveorganic substances and on smooth, rough or porous surfaces, or surfacesof any other form, care must be taken to compensate for the heat lossesoccurring during the metallizing operation, by heating the surface ofthe substance to be metallized to the decomposition temperature from theoutside and constantly supplying heat from the outside during theseparating process. The temperature of the surface of the material mustnot in any circumstances be higher than the temperature of thedecomposition of the metal compound. Experience has shown that this isof particularly great importance in the metallization of organicsubstances, since otherwise the organic substance is damaged and theadhering strength of the deposited layer is greatly reduced. In order tomaintain constant decomposing conditions, it is proposed in accordancewith the invention, in all the decompositions hereinafter described, tomaintain a minimum path of movement of the metal atoms or fine metalparticles from the point at which they are separated from the metalcompound to the point at which they are deposited, that is to say, toensure that the metal atoms or particles pass along the shortest path tothe surface of deposition without having too great an opportunity ofaggregating during their movement, since the finer the depositedparticles remain the better are the molecular binding forces, by whichthey are bound to the surface of the article and by which they areincorporated in the growing metal film, able to take effect. It must beborne in mind that the length of the path of free movement is so smallunder normal pressure conditions that in the separation of metal fromthe compound the danger exists, even in the neighbourhood of thesurface, of the metal particles agglomerating to form coarser particlesbefore they reach the surface. It is therefore desirable either to causethe decomposition actually to take place only immediately on the surfaceof the articles to be metallized or to ensure, when the separation takesplace at a distance from the surface, that the metal atoms or fineparticles pass as rapidly as possible to this surface, by superimposingon their free movement a preferred direction towards the surface. Thisis done by directing a stream of the metal compound at great velocitytowards the surface of the article, it being possible for thedecomposition to take place at a more or less great distance from thesurface.

The working conditions hereinbefore referred to which must be maintainedin accordance with the invention in order to produce completelysatisfactory metal deposits from metal compounds, namely constant,reproducible reaction conditions at the point of separation, heating atconstant temperature preferably only at the surface of the article to bemetallized, and prevention of agglomeration of the metal atoms or veryline particles separated from the metal compound by adjusting the lengthof their path of free movement, constitute in combinauon new workingdirections.

If the decomposition takes place directly on the surface of the articleto be metallized, or at a distance therefrom, it is in all circumstancesimportant that only the surface itself, but not the mass of the entirearticle, be heated because heating of the mass of the article iscompletely unimportant to the metallizing process and involves aconsiderable loss of heat. More especially, if only the surface on whichthe metal compound is decomposed is heated, the conditions ofdissociation can be much more readily maintained uniform and themetallizing process can proceed at great speed over the surface. Thus,only a fraction of the thermal energy otherwise necessary for heatingthe entire article to the decomposing temperature is required for themetallization. Similarly, the time taken by the metallization is only afraction of that taken in the known processes.

The heating of the surface to the decomposition temperature does notpreclude pre-heating of the article below the decomposition temperaturefrom being expedient in special cases.

The manner in which the process according to the invention is carriedinto practice may vary greatly in accordance with circumstances. Theperformance of the process will hereinafter be described by way ofexample with reference to the embodiments illustrated in Figures 1 to'17 of the drawings.

According to Figure 1, a material or article 1 to be metallized isbrought to decomposition temperature at the surface by contact heating,for example by means of the heating elements 2 sliding along the surface(or travelling heating rollers). The contact heating of the surface mayalso be effected by other means, namely by solid, fluid or pulverousheating elements. Arranged between these heating elements 2 are the feedducts 3 for the metal compound, through which the metal compounds areblown in a jet 4 on to the surface. The system 2, 3 is uniformly movedas a whole in the direction of the arrow A in relation to the fixedarticle 1, or vice versa, it being possible to carry out this movementat a very high speed of a few metres per second and nevertheless toobtain a cohesive metal coating of high electrical conductivity. In thismovement according to Figure 1, each successive point of the surface isalternately heated and metallized, so that heat is continuously suppliedfrom the outside to the point in question during the separation(deposition). According to the required thickness of the metal layer, asuitable number of heating elements 2 and metal feed ducts 3 arearranged one behind the other, or the system 2, 3, is repeatedly passedover the article to be metallized.

In Figure 2, the heating of an element 1 to be metallized is indicatedby jets of material (hot gases, vapours, powder), a hot jet of material5 being blown through feed ducts 2a on to the surface. The metalcompound is simultaneously blown in a uniform jet 4 on to the same point6 of this surface through the feed duct 3. Alternatively, the heat andthe metal compound can be alternately delivered for short intervals, forexample with fifty alternations per second. By this continuousalternation, the temperature is maintained constant at the point 6during the separation process. Here again, the mctallizing ar arrowthrougha thin foil in, for example of mica,

rangement 2a, 3 is moved in the direction of the arrow A over thesurface, or vice versa.

As a modification of Figure 2, it is possible as shown in Figure l toheat the surface by replacing the contact heating elements 2 by feedducts 2a for hot jets of material, so thatthe heating jet alwaysprecedes-a jet of metal compound by a short distance.

The stepwise heating of the surface according to the invention makes itpossible, as indicated in-Figure 2, to house the arrangement 2, 3 in avessel 7, which projects thestill hot point just metallizedfrom theadmission of air and consequently from oxidation;

Solids of revolution can be metallized on the surface by heating-thearticle, which-is rotated about its axis, from one side, for-examplebyajet of gas, and blowing-on the metal compound fromthe opposite side.

In-the aforesaid surface heatingby means of jets of material, substancesmay be admixed with such jets of-material in order to effect anadditional heating by chemical or physical. reactions on the surface,such admixed substances being, for example, hydrogen atoms, whichrecombine toform molecules while giving up heat on the surface tobemetallized; Moreover, substances such asfine metal powder may be admixedwith the jet of material by which the surface is heated, in order topromote catalytically the thermal dccornpositionof the metal compound.The catalyst may be, for example, iron powder if iron carbonyl isemployed as the metal compound. A jet of heated, finely distributedmaterial, for example heated metal particles may also be employed toheat the surface, such material being deposited in solid form on thesurface together with the metal deposition. Thus, for example, the knownmetal spraying process may be employed for this type of heat supply.

Thenew process may also be employed'to metallize the innersurface ofporous articles, for example of wood or ceramics.

Such an article is shown at-fiinFigure 3. A hot gas (or vapour) isdelivered at it from a vessel 9 and-penetrates through the article inthe direction indicated-by the arrow, and heats the inner surfacethereof. Thereafter, Orin continuous alternation withthe said gassupply,the metal compound is passed throughthe porous article at Intheembodiment shown in Figure 4, a continuous heating of the inner surfaceof: anon-conductive porous element 8 isefiected bythe applicationof twolattice-like electrodes 12, between which an electric discharge (forexample high-frequency) takes place.

Figure 5 shows by way of example the dielectric heating of the surfaceof a non-conductive article 1. This article has a. surface layer 13having higher dielectric losses thanthe article 1, so that the heatingof. the article 1- disposed between the electrodes 14 and l5islimitedsubstantially to the surface layer 13.

If desired, the surface of an articlemay be inductively heatedwithout-the aforesaid surface layer 13;

In the embodiment shown in Figure 6, the. surfaceof the article 1isheated by electronic and/or ionic impact, the electrons emanating froma heating filament 16. This method of heating affords the advantage thatthe heating islimited to very small area 17 byv screening of theelectron beam asshown in the drawing,,so that punctiform or lineatedmetallisation can be effectedwith this electronic impact heating.

A certain depth effect is obtained in the heating by electronic or ionicimpact, so that metal compounds diffused into the surface are depositedin a certain surface layer. This iii-particularly advantageous for agood anchoring of a metaldeposit. The metal compoundis delivered-at 3.

While in Figure discharge, 7bya-discharge, in this case an are 18, anintensiveheatingtof the surface being effected both by the. heat of thearc and by the ions and electrons in the neighbourhood thereof. Inthiscase, the arc is blown on to the surface by the: core of a blowingmagnet energised by the magnetcoil 20.

Figure 8 shows a particular case of the application of the absorption ofthe energy of electrically charged and accelerated corpuscles whichemanate from aheating filament land penetrate in the direction indicatedby tlge t0 6 6 the surface is directly heated by a At the outlet point,the metal compound metallised.

it maybe indirectly'heated according to Figure fed thereto from theopposite side at 3 is decomposed by the impact energy of the corpuscles;In the first metal layer thus formed, the corpuscles are completelyabsorbed with temperature increase. This produces further thermaldecomposition of the metal compound fed thereto.

In Figure 9 an embodiment is shown in which the surface is heated byelectromagnetic radiation, for example infra-red or short-waveradiation. The metal compound is delivered at 3 tea bell-shapedcontainer 21. The infrared radiation indicated by the arrows Bpenetrates through the closure plate 22, consisting of rock salt or thelike, of this con'tainer to the surface of the article 1, so that thissurface is continuously heated during the deposition of the metal.

Figure 10 shows diagrammatically a particularly economical method ofmetallizing an article 1 which already has a conductive surface 23 andwhich has been metallized, for example, by one of the aforesaid methods.Electrode rollers 24 are moved over the surface of this element at adistance apart, the said rollers being connected to a source of current25, so that the surface layers 23" lying between these electrodes arebrought by resistance heating to. the decomposition temperature.Resistance. heating may also be employed to metallize porous. articlesalready having a conductive inner surface as shown in Figure 4.

The surface heating may also be effected with supersonic oscillations,for example by transmitting oscillations by means of a quartz crystal 26to anarticle 2S tapering to a point 2? or knife edge, as shown in Figure11. The friction of the point 2'7 on the surface of theelement 1produces a high local. heating which decomposes the metal compounddelivered at 3..

In themetallization of materialsor articles by. heating and depositiondirectly on the surface, the metallization may be effected in vacuoinspecial cases, forexample. in the metallization of very smoothsurfaces, one of. the methods already described. being. applied.Generally, however, the new metallizing process will be most:economically carried out.- at atmospheric pressure.

While the methods described. in: the foregoing examples effect.fundamentally a heating and deposition on the surface of the. article tobe metallized,.the process according to, the invention. can also becarried out,. as illustrated by way. of example in Figures 12 to 14- byelfecting the decompositionof the. metal compound,.not on the surface,but at a distance. a therefrom. In order to prevent the agglomeration ofthe metal atoms or particles in the movement alongthe path atothesurface, these metal particles must be blown onto the surface atgreat speed, for exampleat a few m. persecond. Theorder of magnitude ofthe distance a is in, this case of a few millimetres.

According to Figure 12, the metal compound is delivered, at. 3 at thishigh speed, thev issuing; metal compound-being guided in the vessel 29through a heating ring 30 so that the metal compound is decomposed'bythe heating action thereof.

According to Figure 13, the metal compound, for example nickel carbonyl,is under high pressure (about 100 atmospheres absolute pressure) in. apressure-proof container 31 which is brought by means of an electricheating element 32 to a temperature (for example 240 C.) lying above thedecomposition temperature of the metal compound at normal pressure. Themetal compound is blown at high speed on to the surface of the article 1through an outlet aperture 34 adapted to be. closed by a cone valve 33or the like. Theexpansion occurring at the discharge of themetalcompound'brings the metal compound out' of the stable conditioninto. the unstable condition, so that it is decomposed.

Inthe example shown in Figure 14; the metal compound is introduced at 3.through a non-return valve 35 into a container 36 in which intensivespark discharges occur in rapid succession between the electrodes 37.The metal compound is decomposed by these spark: discharges and theproducts of decomposition are at the same time blown by the explosiveeffect at very high speed through the aperture 38 on to the surface ofthe article, th'isblowing-on .of the metal particles takingplaceintermittently.

Again inFigure 15, such an intermittentdelivery. takes place, not of themetal particles, but. of the metal compound delivered at 3 into thecontainer 39. This intermittent delivery to the surface of the article 1is procompound is delivered to the surface during the metallization, itis possible in accordance with Figure 17 to apply the metal compoundindicated at 42 previously to the cold surface of the'article 1. Itadheres to the surface, and is diffused into or dissolved in the saidsurface, or rests thereon below a protective film which preventsit"from'rapi'dly evaporating. The heating is effected by the heating jet5.

In carrying the process according to the invention into practice, allmetal compounds may be employed which are dissociated into metal andresidual substance under the action of heat. Such compounds are mainlymetal carbonyls, metallic hydrides and metallic halogens. Examples ofmetal carbonyls are nickel tetracarbonyl, iron pentacarbonyl and thecarbonyls of tungsten, molybdenum and cobalt. The hydrides which may beemployed include, for example; copper hydride, germanium hydride,antimony hydride and others, while the chlorides includechromium'chloride and nickel chloride, and the other types of compoundswhich may be employed include particularly metallic acetyl acetonatessuch as copper acetyl acetonate. In addition to these compounds whichcan be directly separated under heat, metal compounds which liberate themetal on reduction or chemical reaction by thermal means may also beemployed for the metallizing process according to the invention. Asexamples for the reduction method may be mentioned the oxides of theprecious metals and of other heavy metals, and for the chemical reactionmethod the halogen compounds of the heavy metals, for example chromiumchloride, are particularly suitable.

The process according to the invention may be employed inter alia toproduce metal deposits on compact articles or on and in porous articlesor materials. One of the characteristic features of this process residesin the fact that the quantity of metal deposited per unit time issubstantially greater than in the metal vaporiza' tion process and iseven greater than in the galvanic process. Moreover, metallic depositscan be applied by means of the process to bright, oxidized or otherwisecoated metals, and especially to non-metals such as plastics, wood,fabrics, papers of all kinds, felts, fibres of organic and inorganicnature, glass, quartz, ceramics, salts and other compounds, that is tosay, to all solid or plastic materials whose surface does not undergoany detrimental physical or chemical modification during the metallizingoperation.

Extremely fine projections or pores can be filled by the metal deposit.Sensitive organic substances are also not damaged if the metallizationprocess is correctly conducted. For example, papers, textiles and thelike may be coated on their outer and inner surfaces with a metal filmwhich embraces each individual fibre and which, if of suitablethickness, cannot be mechanically detached without partial destructionof the fibres.

The metallization is so clean and true to the surface and adheres sostrongly that it can be used as a support for a further galvanicdeposition of any desired metals. For this purpose, only an extremelythin layer deposited by the process described is required in the case ofmetallized non-conductors.

Naturally, the conductive layers deposited from the gas phase have, ascompared with the layers hitherto produced by the deposition of silveror by the application of layers of graphite or silver sulphide coatingsby the wet method, an immeasurably greater adhering strength which canonly be compared to the ideal attachment of fine-grained deposits by thecathode atomization or vaporization process. Since the economy of theprocesses for the separation of metals from compounds according to theinvention is nevertheless considerably greater and it must be taken intoaccount that the adhesive strength of a conductive layer on anonconductor is essential to the adherence of the metal filmsubsequently galvanically deposited, the process is also of particularnnportance in the electroplating field.

I claim:

1. Process of depositing a uniform firmly adherent coating of metallicparticles of finely divided sub-crystalline size upon the surface of abase material which comprises heating the surface of said base materialin successive small increments of surface area to a substantiallyconstant temperature and not substantially above the decompositiontemperature of a heat decomposable metallic compound and projecting jetscontaining such decomposable metalliccompound onto said heated surfaceto effect concomitant decomposition of said compound and coating of thesurface, said heat and jets of metal compound being supplied to eachsmall increment of surface area to' be metallized in constantalternation and in rapid succession whereby the temperature of thesurface being metallized ismaintained evenly during the entiredepositing process and the metal particles deposited on said surface arein sub-crystalline size.

2. The process as defined in claim 1, wherein the object to be coated isthin sheet material and the jets of decomposable metal compound areapplied to one surface thereof while the heat is applied to an oppositesurface thereof in rapidly alternating jets applied to small incrementsthereof.

3. Process of depositing a uniform firmly adherent coating of metallicparticles of finely divided sub-crystalline size upon the surface of anon-metallic base material of relatively low heat conductivity whichcomprises heating the surface of said base material in successive smallincrements of surface area to a substantially constant temperature andnot substantially above the decomposition temperature of the heatdecomposable metallic compound and projecting jets containing saiddecomposable metallic compound onto said heated surface to effectconcomitant decomposition of said compound and coating of the surface,said heat and jets of metal compound being supplied to each smallincrement of surface area to be metallized in constant alternation andin rapid succession whereby the temperature of the surface beingmetallized is maintained evenly during the entire depositing process andthe metal particles deposited on said surface are in sub-crystallinesize.

4. The process as defined in claim 1, wherein the base material to becoated is organic.

5. The process as defined in claim 1, wherein the base material to becoated is inorganic.

6. The process according to claim 1, wherein the metal compound ispreheated to a temperature below the decomposition temperature.

7. The process according to claim 1, wherein the metal compound isapplied by supersonic convection flow upon the surface to be coated.

8. Process as defined in claim 1, wherein the base material to bemetallized is porous, the compound of a heat decomposable metal beingsupplied to the porous body together with an electric discharge, theheat decomposable metal compound being passed through the porous bodyand the electrical discharge serving to heat the inner porous surfacesthereof to effect metal deposition therein.

9. Process as defined in claim 1, wherein a jet of hot materialcontaining a finely divided catalytic substance adapted to reduce thetemperature of decomposition of a heat decomposable metallic compound issupplied to the surface to be coated together with the heat decomposablecompound for metallizing thereof.

10. Process as defined in claim 1, wherein the surface to be metallizedis first coated with material having higher dielectric losses than thematerial to be metallized and the material to be metallized is heated byinduction heating while supplying thereto the heat decomposable metalcompound, whereby the heating is limited substantially to the surfaceportion of the material to be metallized.

11. Process as defined in claim 1, wherein the article to be metallizedis heated by electro-magnetic radiation.

12. Process as defined in claim 1, wherein the surface of the article tobe metallized is coated with a conductive material and the surface isthereafter heated to the decomposition temperature of a heatdecomposable metal compound to be coated thereon by heating saidconductive material by electrical resistance heating.

13. Process as defined in claim 1, wherein the surface m tall zed, pos tt of the metal Particle b depositcd,,, the ar icle o be me a li edi eina12p. ,..eab

to. the; e t'rvqn l x harged. Patt 's; a

:5... Pr ce s as, defined cl im Lwheteiw meta omtaoun s herma y; slmpcsedi subst l I ita dist ncem th s rfa e pct l z d a p o compound are.blown onto, the. suriface 'to be metalliz'ed tiathigh spe e d ng about 9met rs-Pe se on 16 Process as defined in claim 1, whereihthe heatdecomposable metal compound is decomposed, explosively substantially ata distance from the surfiaee to berrietallized and the products ofdecompositionare simultaneously blown onto said surface' 17 Process asdefined in claim 1, wherein the heat decomposable metal compound issprayed onto the-surface to be metallized by contact with anelementoscillating at supersonic frequency.

18. Process as defined in claim 1, wherein ajet of hot finely dividedmetal particles is supplied, asa source oi heat alternately with theheat decomposable, metal cornpound, the finely divided hot metalparticles being=deposited as a coating of metal upon the base beingcoated together with the extreme fine metal formed by decomposition ofthe heat decomposable metal compound.

cts of deco'mposit'on of the he it decomposable metal hot a '-i ui n+ es ourc of, h tte st e l t .t i it s rfa e hea ed, a e substanti ll s ite i q mpe eli tsbein an s 'alte 1y ari'd in sequence progressively toeach part otfthteisur ee a imof sma inqteme ts r ac T a ea and a p11 lY- jets the met l ebh pqund one for ea h nously applied over successivesmall increments of is BefflfimesCited mhefi s. o t this ats ts UNITED:STATES :BATENTS 1, 8;, 9 QhQQR -v b- 9.,,19 2 1 3 7 .41 fi vl 'c a1 e t9.; 19 2 233,304,. Blealgley eb, 2 1941 3 ,0 5,509 Germer et a .May. 23;1950 2,576,289 rl. Q 1.19 1 26125433 Da s t a1- 1? New 2 .952 2;63l,'948. Belitz et a1. ,Mar. 17; 1253

1. PROCESS OF DEPOSITING A UNIFORM FIRMLY ADHERENT COATING OF METALLICPARTICLES OF FINELY DIVIDED SUB-CRYSTALLINE SIZE UPON THE SURFACE OF ABASE MATERIAL WHICH COMPRISES HEATING THE SURFACE OF SAID BASE MATERIALIN SUCCESSIVE SMALL INCREMENTS OF SURFACE AREA TO A SUBSTANTIALLYCONSTANT TEMPERATURE AND NOT SUBSTANTIALLY ABOVE THE DECOMPOSITIONTEMPERATURE OF A HEAT DECOMPOSABLE METALLIC COMPOUND AND PROJECTING JETSCONTAINING SUCH DECOMPOSABLE METALLIC COMPOUND ONTO SAID HEATED SURFACETO EFFECT CONCOMITANT DECOMPOSITION OF SAID COMPOUND AND COATING OF THESURFACE. SAID HEAT AND JETS OF METAL COMPOUND BEING SUPPLIED TO EACHSMALL INCREMENT OF SURFACE AREA TO BE METALLIZED IN CONSTANT ALTERNATIONAND IN RAPID SUCCESSION WHEREBY THE TEMPERATURE OF THE SURFACE BEINGMETALLIZED IS MAINTAINED EVENLY DURING THE ENTIRE DEPOSITING PROCESS ANDTHE METAL PARTICLES DEPOSITED ON SAID SURFACE ARE IN SUB-CRYSTALLINESIZE.